1. Field of the Invention
The present invention relates to a fuel injection control device of an engine.
2. Description of the Related Art
In a known engine, the amount of air Q fed into the engine cylinders is detected by an air flow meter, and the engine speed Ne is detected by an engine speed sensor. The amount of air fed into the engine cylinders per one revolution of the engine Q/Ne (=QN) is calculated from the output signals of the air flow meter and engine speed, and the basic fuel injection time is calculated from QN. The actual fuel injection time is determined on the basis of the basic fuel injection time (see Japanese Unexamined Patent Publication No. 57-200632).
When the engine is started, the inner wall of the intake port is normally dry, and consequently, when fuel is first injected from the fuel injector, a large part of this fuel is used for wetting the inner wall of the intake port, and only a small part of the fuel is fed into the engine cylinders. Therefore, in the above-mentioned engine, to feed a sufficient amount of fuel into the engine cylinders, the basic fuel injection time is corrected so that the actual amount of fuel injected by the fuel injector is increased.
Further, when the engine is decelerated after the engine is started, since a high vacuum is produced in the intake port, a large proportion of the fuel adhering to the inner wall of the intake port is vaporized, and thus the air-fuel mixture fed into the engine cylinders becomes excessively rich. Note, the above-mentioned QN indicates an engine load, and thus QN becomes small when the engine is decelerated. Therefore, whether or not the engine is decelerated can be judged from a determination of whether or not QN is changed, i.e., QN is decreased. Consequently, in the above-mentioned engine, to prevent an excessively rich air-fuel mixture, the basic fuel injection time is corrected so that the actual amount of fuel injected by the fuel injector is reduced by an amount corresponding to a changing rate .DELTA.QN of QN.
In this engine, if QN is changed only when the engine is decelerated, it is possible to continuously feed an air-fuel mixture having an optimum air-fuel ratio into the engine cylinders by reducing the actual amount of fuel injected by the fuel injector in accordance with a change in QN. But, in this engine, when the engine is started, since QN is reduced even though the engine is not decelerated, the actual amount of fuel injected by the fuel injector is reduced, i.e., upon engine start up, when the engine is rotated under its own power, the engine speed Ne is rapidly increased, but at this time, the amount of air Q fed into the engine cylinders remains substantially unchanged, and consequently, at this time, QN is rapidly reduced. As a result, since the actual amount of fuel injected by the fuel injector is reduced as soon as the engine is rotated under its own power, a problem occurs in that the engine stalls.